The present invention relates generally to road wheels for track laying vehicles and particularly to a hybrid wheel structure that has both low mass-moment of inertia and high strength. A road wheel is distinguished from a drive wheel and idler wheels of track laying vehicles in that the drive wheel is a sprocket device that engages track lugs to translate the track and thereby move the vehicle. Idler wheels are located beneath the upper horizontal extent of the track to support the upper extent against vertical sagging.
In order to lighten the road wheels, which receive the "ground load" from the tracks of track laying vehicles, and thereby lighten the vehicle on which the wheels are employed, a variety of proposals have been made. In U.S. Pat. No. 4,349,234 to Hartmann an all aluminum wheel is disclosed, whereas U.S. Pat. No. 4,607,892 to Payne et al. proposes the use of all aluminum or all fiber reinforced resin wheels.
In reviewing materials and manufacturing proposals for making road wheels a number of important considerations are needed. Aluminum road wheels, for example, comprise two back-to-back, deep, cup-shaped cylinder structures that are made by deep forging of heated aluminum work pieces. "Hot" forging processes require special dies and costly special forging alloys that are needed to withstand the severity of the forging process.
The all fiber reinforced composite wheel, which has a lighter density than aluminum alloys, may not necessarily be lighter in weight than an all aluminum wheel. This is because the fiber reinforced material does not have the strength and performance capabilities of aluminum. A greater amount or volume of fiber reinforced material is therefore generally needed to meet performance requirements.
For example, the loads in the area of the hub of a road wheel are substantially greater than in the rim area. In order to care for strength and performance in the hub area, when using fiber reinforced materials, it is necessary to increase the thickness of the fiber reinforced materials. Hence, in an all composite wheel, the savings in weight provided by its lower density may be offset by the increase in the volume of composite material needed to meet performance requirements.
Composite materials are generally more costly than aluminum alloys. The cost per pound of composite materials for these kinds of application is generally two to three times more expensive than appropriate aluminum alloys. Hence, the material of an all fiber reinforced wheel would appear to be substantially more expensive than an all aluminum wheel. However, comparative costs of the two wheels tend to equalize because of the higher manufacturing costs involved in deep forging aluminum workpieces to form the cup shape of the road wheel.
In the case of the above Hartmann patent, continuous steel rings are employed as wear resistant surfaces in the cleat receiving groove of the wheel. This locates the heavier masses of the steel rings in a position of the wheel that increases its mass moment of inertia, rather than decreasing it. In the Payne et al. patent, continuous wear rings are made of a resin matrix containing such materials as graphite, shot, particulate steel or ceramic. The rings are permanently secured to or integrally formed with the structure of the wheel. If such a ring is worn or damaged, the entire wheel is replaced in order to replace a worn ring with a new one.